There are great pictures of pahoehoe in Day 2.<\/li>\n<\/ul>\n\n\n\nWe visited a road-cut that featured an infilled lava channel, with columnar jointing and surface oxidation.<\/p>\n\n\n\n
At stop 7 we saw very thin pahoehoe flows. Olivine rich at top, olivine poor at bottom. You can see the tubular structure of the pahoehoe flows. <\/p>\n\n\n\nStructure of pahohoe flow showing tube formation and oxidation (left); olivine-rich basalt (right)<\/figcaption><\/figure>\n\n\n\n<\/span>Notes on hydrothermal alteration <\/span><\/h3>\n\n\n\nSteam is altering the basalt. This is metasomatism \u2014 hydrothermal alteration \u2014 where the minerals\u2019 compositions are altered i.e. the chemicals present in them are changed due to the hydrothermal fluids and gasses.<\/p>\n\n\n\n
The white stuff is \u201csinter:\u201d The most common form of sinter is silica sinter, which is made primarily of silica (SiO\u2082), though it can also contain other minerals depending on the composition of the geothermal fluids. There is also some calcite. This system is near neutral \u2014 elsewhere you\u2019ll have more acidic. That will produce phosphate and sulfide minerals. These are often implicated in ore formation.<\/p>\n\n\n\n
We are seeing steam-heated overprinting that is producing kaolinite. In geological terms, an “overprint” refers to a secondary mineralization or alteration event that affects a pre-existing rock or mineral deposit. In this context, it means that steam is modifying the plagioclase in basalt to kaolinite. This is one reason that in figuring out the geological history of an area you have to map \u2013 the composition of the rock is not enough.<\/p>\n\n\n\n
Hydrothermal systems associated with ring faults are self- reinforcing systems. The alteration weakens and exacerbates the faults, which in turn creates or widens channels that allow steam to emerge.<\/p>\n\n\n\n
<\/span>Day 2 (1\/25): Kilauea fountains & stratigraphy<\/span><\/h2>\n\n\n\n<\/span>The First Eruption<\/span><\/h3>\n\n\n\nFirst eruption in Halema\u02bbuma\u02bbu, from the caldera rim<\/figcaption><\/figure>\n\n\n\nAt the Kalauea caldera we arrived to find an eruption in progress. We are seeing lava fountaining and lots of smoke. The column of smoke was amazing to see \u2013 quite beautiful! The geologists are reading the (slight) colors in the plume and inferring which volatiles are degassing.<\/p>\n\n\n\n
Pele\u2019s hair (sideromelane).<\/strong> There is golden Pele\u2019s hair on the ground. Pele\u2019s Hair is made of a glass called sideromelane. Golden Pele\u2019s Hair was quenched at a high temperature before iron oxice crytlas could form; brown Pele\u2019s Hair cooled more slowly, allowing time for some crystallization. In the presence of water, Pele\u2019s Hairwill alter to palagonite.<\/p>\n\n\n\nSomeone brought (and shared) binoculars, which provided a very nice view of the rift, lava lake, pahoehoe flows, and other features.<\/p>\n\n\n\n
NOTE: Caldera Collapse does not occur AFTER the Eruption \u2014 rather eruption and collapse are synchronous. Ancient caldera collapses are indicated by mega-breccia.<\/p>\n\n\n\n
<\/span>Base Surge Stratigraphy: crossbedding lapilli, bombs, and ripples<\/span><\/h3>\n\n\n\nThe penultimate stop was also excellent. We went along the closed section of Crater Rim Road (starting from the Desolation Trailhead). This offered another view of the eruption. There was also a spatter rampart, built of glossy glassy blobs of lava \u2013 I think the name of this rock\/texture was \u201cagglomerate.\u201d<\/p>\n\n\n\n
Right at the point where the road is blocked off there are ash layers, etc., produced by a base surge (a pyroclastic eruption which projects materials in all directions). More of these features will be visible in the Ka\u2019u desert hike on Day 3.<\/p>\n\n\n\n
It was interesting to see how well the geologists could \u2018read\u2019 the layering. We saw crossbedding (right), and (below) accretionary lapilli, bombs and ripples.<\/p>\n\n\n\nBase surge stratagraphy: accretionary lapilli in strata (left); rippled ash bedding (right)<\/figcaption><\/figure>\n\n\n\n<\/span>Base Surge Facies<\/span><\/h3>\n\n\n\nDiagram of base surge facies<\/figcaption><\/figure>\n\n\n\n<\/span>Day 3 (1\/26): Kau Desert: A\u2019a, pahoehoe, Pele\u2019s Hair, Ash and Lapilli<\/span><\/h2>\n\n\n\nThe hike starts out in an a\u2019a lava field and then transitions to a different flow that is largely pahoehoe. This area has really beautiful examples of ropey pahoehoe.\\<\/p>\n\n\n\nLovely pahoehoe<\/figcaption><\/figure>\n\n\n\nTwo other images show the imprints of spatters of lava drops, and tortoise shell cracking. \u2026and one accretionary lava ball from the a\u2019a section of the hike because I had room\u2026<\/p>\n\n\n\nTortise shell cracking (left), lava drop impressions (center), accretionary lava ball (right)<\/figcaption><\/figure>\n\n\n\nLayers of lithified ash showing crossbedding (left), and ventilation effects from wind across wet ash (right)<\/figcaption><\/figure>\n\n\n\nAccretionary lapilli (right) and Pele’s hair (left) in Ka’u desert<\/figcaption><\/figure>\n\n\n\nI was dismayed that, by the end of this hike which was no more than 5-6 miles, I was feeling a lot of fatigue.<\/p>\n\n\n\n
<\/span>Day 4 (1\/27): Lava field with lava trees; and a spatter rampart<\/span><\/h2>\n\n\n\n<\/span>Lava field, with trees<\/span><\/h3>\n\n\n\nThe day began with a drive down Chain of Craters road. Our first stop was at a site near Devastation Trailhead, next to a pit crater, that had lava trees \u2013 that is, lava had flowed around tree trunks and cooled against their surfaces, forming blocky pillars, often with a cast of the trunk inside (and, occasionally, with some of the tree remaining). This flow happened in 1974.<\/p>\n\n\n\nWe had to go about an eighth of a mile to find the lava trees, and as we did so we found that we could see that this was a very small lava field, and that we could see all of its features. We found the vent from which the eruption began along with a spatter rampart (whose asymmetry shows the direction of the wind during the eruption), the slabby pahoehoe that is characteristic of near-vent flow, and the main lava channel that drained the field into a nearby pit crater in a lava fall.<\/p>\n\n\n\n<\/span>Rift, with spatter rampart<\/span><\/h3>\n\n\n\nOur second stop was Napau Trailhead, which provides an excellent look at a rift, with spatter ramparts and drainback features. This spatter rampart was formed in about a day.<\/p>\n\n\n\n
Rift (with vegetation), and spatter ramparts to its left (indicating a strong wind blowing in that direction):<\/p>\n\n\n\nSpatter ramparts are cool because they have lovely textures from the agglomeration of spatter, which often oxidizes into reds and orange colors, and has glassy surfaces because of rapid cooling.<\/p>\n\n\n\n\u2003The protrusion below is likely a deflation feature, left behind as the level of lava dropped through draining and shrunk, through cooling. (Al originally thought these were hornitos, but George the volcanologist did not agree).<\/p>\n\n\n\nSpatter rampart terminology: Juvenile fragment == spatter; accessory fragment == a solid ejected from the rift; accidental fragment == anything not associated with the source of the lava such as a xenolith or local rock.<\/p>\n\n\n\n
<\/span><\/span><\/h3>\n\n\n\nAt the end of the day, we had dinner in the bar at Volcano house. During dinner the eruption started again. At first all you could see was smoke reflecting an orange glow below, then there was a small bright spot that pulsed about once a second. Overtime the spot grew into a long curtain-like fountain that grew higher and higher. As this happened you could see a glow spreading out from its base, a growing lake of lava. As the fountain increased in size, the erupting lava fell on the slope from which it is erupting, and flowed rapidly downhill in three streams.<\/p>\n\n\n\nFrom the caldera below, steam is rising in billows that mirror the cloudy sky.<\/p>\n\n\n\n
<\/span><\/span><\/h2>\n\n\n\n<\/span>Second episode of the eruption, continued<\/span><\/h3>\n\n\n\n<\/span>Napau trail to Mauna Ulu Shield<\/span><\/h3>\n\n\n\nThe plan for the morning was to return to Napau Trailhead, where we were yesterday, and hike the trail to the Mauna Ulu Shield. Mauna Ulu is a small shield volcano \u2013 known as a satellite or parasitic volcano — in Kilauea\u2019s East Rift zone that was formed by a series of eruptions from 1969 to 1974. It features pahoehoe, a perched lava lake, lava channels, and a crater so deep that we were unable to see the bottom (being wary of getting too close to the edge). On the way there we took a side-trip to Pu\u2019u Hulu Hulu, a fern-filled crater so inaccessible that even wild pigs can\u2019t get there; as a consequence, it is an orchid refuge.<\/p>\n\n\n\n
<\/span>Day 6 (1\/29): Kilauea Iki and flux banding<\/span><\/h2>\n\n\n\n<\/span>Kilauea Iki<\/span><\/h3>\n\n\n\nThe eruption of the Kilauea Iki pit crater in 1959 created a lava lake approximately 130 meters deep. Over the next three decades, the U.S. Geological Survey (USGS) scientists conducted detailed studies\u2014drilling into the solidifying lava lake to measure temperature profiles, sample cores, and observe the crystallization processes. They discovered that the newly formed basaltic layers continued to circulate internally for a surprising length of time, demonstrating that cooling lava can remain dynamic and chemically evolving well after the surface solidifies. Their research also showed how minerals separate out (fractional crystallization) in basaltic magma chambers, and how gas content, cooling rates, and layering patterns influence the final rock textures.<\/p>\n\n\n\n
We hiked into the crater and across the now-solidified lava lake. We saw the vent from which the lava erupted, the main lava channel, and the lake itself. The surface of the lake showed polygonal cracking, with, occassionally, lava \u2018squeezing up\u2019 through the cracks. The lava lake also exhibited \u201coverturn,\u201d where the cooling lava on the lake\u2019s surface becomes unstable because of its growing density, and at various points a wave of overturning sweeps the lake and leads to \u201cresurfacing.\u201d<\/p>\n\n\n\nAt a larger scale we could see lava islands\u2013portions of collapsed wall that had fallen into the lake (left) \u2013 and lava \u2018bathtub rings\u2019 (not shown). It was also interesting to see Ohia trees colonizing the lava, growing out of cracks in the basalt.<\/p>\n\n\n\n<\/span>\u2003<\/span><\/h3>\n\n\n\nIn the afternoon we went to examine a fault zone. I didn\u2019t get a lot out of this, but I did notice some unusally patterned basalt and asked about it. I learned that the pattern is called flux banding, and happens as lava or magma is moving over a surface that creates shear; this is exacerbated when the lava includes phenocryst.<\/p>\n\n\n\nAbout Fluxion Banding from ChatGPT: <\/p>\n\n\n\n
\n“Fluxion banding is a type of flow-related texture observed in volcanic and intrusive igneous rocks, particularly in lavas and some plutonic settings. It forms due to the differential movement of molten or partially molten material, creating distinct bands of varying mineral composition, crystal size, or vesicularity.<\/p>\n\n\n\n
“Fluxion banding results from shear forces within a moving magma body due to:<\/p>\n\n\n\n
\nDifferential Flow in Lava \u2013 As lava moves, its viscosity varies due to cooling and crystallization. The outer layers, which cool faster, may develop a plastic or solid crust, while the inner material remains fluid. This difference in viscosity causes layers of magma to stretch and deform, forming elongated bands.<\/li>\n\n\n\n Crystal Sorting and Alignment<\/strong> \u2013 As magma flows, mineral crystals within it may become aligned due to shear stress. This is common in silicic lavas like rhyolite and dacite, where feldspar and quartz can form parallel bands.<\/li>\n\n\n\nMagma Mixing and Compositional Banding<\/strong> \u2013 If two magmas of different compositions mix, they may not completely homogenize, leading to streaks of contrasting compositions that appear as bands.<\/li>\n\n\n\nIntrusive Settings \u2013 In some plutonic rocks, fluxion banding may form as a result of late-stage magmatic flow, where crystals and melts segregate due to convection or deformation.”<\/li>\n<\/ol>\n<\/blockquote>\n\n\n\nThe day ended at Hilina Pali overlook \u2014 it was a lovely place, and immensely quiet.<\/p>\n\n\n\n
<\/span>Day 7 (1\/30): A rainy day for reading<\/span><\/h2>\n\n\n\nIt was raining very heavily in the morning, so we stayed in; I ended up reading quite a bit of the Walker paper o Basaltic Volcanoes. The rain lightened in the afternoon, so we went down to Hilo and saw Akaka falls, and then had dinner at the Ola Brewhouse.<\/p>\n\n\n\n
<\/span>Day 8 (1\/31): Lava diversion; black sand; Fissure 8<\/span><\/h2>\n\n\n\nThe day began with periods of torrential rain and wind, plus intense fog; it began to let up around 8:30am. We visited various sites in Northeast Haswaii: We visited the recycling plant that was almost overrun by lava, and looked at how a chain link fence served to (partially) block it. We had a short discussion about lava diversion, and that using a ^ form facing the direction of flow is most effective.<\/p>\n\n\n\nWe also visited some black sand beaches and it was interesting to see that the sand includes olvine grains. Also got smoothies at a local place.<\/p>\n\n\n\n
<\/span>Fissure 8<\/span><\/h3>\n\n\n\nThe we went on to Leilani Estates and Fissure 8 \u2013 by this time the nasty weather had abated. Our hosts (the Walkers?) enabled us to do the hike to the top of cone around fissure 8, and to view the heavily oxidized interior; on the way back I collected several pieces of reticulite, a stone (or glass) essentially composed of lava foam.<\/p>\n\n\n\n
Fissure 8 produced a big a\u2019a\u2019 flow. A\u2019a flows can be divided into basal breccia; top breccia; flank breccia, with a core of unbroken flowing lava. This sort of layered structure\u2014brecciated at the surface and the base with a more solidified interior\u2014is what makes a’a flows stand out in contrast to smoother, rope-like pahoehoe flows.<\/p>\n\n\n\n
The eruption of fissure 8 also produced a lot of tephra which forms the elongated \u2018cone\u2019 around the fissure; the bottom of the fissure is \u2018paved\u2019 with pahoehoe. Fissure 8 was one of 24 fissures that opened during the 2018 eruption.<\/p>\n\n\n\nHere is a close-up of the tephra produced in the eruption (picture width: ~3 cm):<\/p>\n\n\n\n<\/span>Day 9 (2\/1): The Helicopter tour<\/span><\/h2>\n\n\n\nThe helicopter tour was pretty lackluster \u2013 a dropping cloud cover prevented us from going very high. We couldn\u2019t even get an areal view of fissure 8, let alone the Kilauea caldera. We did get a good look at Eastern Hawaii, and the various lava flows \u2013 there were some pleasing textures and patterns.<\/p>\n\n\n\n
I particularly liked the jig-saw-like texture of the forest and the way the canopy shows inter-tree boundaries:<\/p>\n\n\n\nTrees that exhibit this phenomenon are called \u201ccrown shy.\u201d These may be Ohia trees, but I\u2019m not certain of that.how much they resemble rivers; here, as well, are areal views of a\u2019a and pahoehoe:<\/p>\n\n\n\nAfter the tour we had a late lunch at punalu\u2019lu bakery, and then went on to South Point, where we found some patches of green sand, without having to make the trek to the green sand beach which we didn\u2019t have time for.<\/p>\n\n\n\n
<\/span>Day 10 (2\/2): Hawai\u2019ite, Phreamagamtism and Peperite<\/span><\/h2>\n\n\n\nThe trip is now shifting its focus away from Kilauea to the other volcanoes: Maua Loa, Mauna Kea and Kohala. The latter two, in particular, are transitioning to their post shield phases, and as a consequence are producing more alkaline lavas, and hence more cinder cones and ash. It is fun to look at the distant profile of Mauna Kea and see how \u2018bumpy\u2019 it is \u2013 those are cinder cones produced by the more viscous alkaline lava.<\/p>\n\n\n\n
<\/span>Hawaiite<\/span><\/h3>\n\n\n\nWe visited a point on the north coast where there is a flow of Hawaiite into the ocean. I believe it was from Mauna Kea, but am not certain on that. [check] One of my interests on this trip is seeing the different forms of basalt, and the degree to which they can be distinguished visually. Hawai\u2019ite is definitely lighter in color than thoeltic basalts, and its vesicles, from the examples I have seen, are generally larger as would be expected from its higher viscosity.<\/p>\n\n\n\nDescription: Hawaiite is a relatively evolved type of basalt, meaning the magma that produced it has undergone fractional crystallization, resulting in a higher alkaline content (Na and K), and a somewhat higher silica content. This makes it more viscous, with larger vesicles, and lighter in color than the thoelitic basalts. Hawaiite is commonly characterized by the presence of minerals such as plagioclase feldspar, augite, olivine, and sometimes magnetite.<\/p>\n\n\n\n
<\/span><\/span><\/h3>\n\n\n\nThe structures produced by the more alkaline lavas are not to be confused with the structures produced by phreamagmatism — eruptions involving the interaction of magma or lava with external water (groundwater, lake water, or seawater). These include tuff cones, tuff rings, maars (diatremes), litoral cones, and rootless cones.<\/p>\n\n\n\n
Types of phreamagmatic structures:<\/p>\n\n\n\n
\nTuff cone<\/strong>: Steeply-sloped relatively small cone of fine-grained ash and volcanic debris that forms around a central vent; their deposits often reflect repeated pulses of wet ash fall, which can produce well-bedded, fine-grained tuffs. The steep slope is because the wet fine-grained ash tends to cohere. Tuff cones form when magma interacts vigorously with water at or very near the Earth\u2019s surface. Diamond Head on Oahu is an example\u2014its name comes from calcite crystals which were formed later\u2026 the abundant calcium coming from its eruption the coral and limestone. A subaqueous tuff cone is known as a Surtseyan cone.<\/li>\n\n\n\nTuff ring<\/strong>” Tuff rings have gentle to moderate slopes (often <20 degrees) and are usually wider and have deeper craters relative to tuff cones. Tuff rings typically represent longer-lived phreatomagmatic eruptions that occur below (but still near the surface). They deposit layered, ash-rich tuffs in relatively thin, laterally extensive beds.<\/li>\n\n\n\nMaars<\/strong> typically have a large, wide, deep crater with a low rim composed of ejected volcanic fragments; the crater floor of a maar often lies well below the original ground surface. Maars form from deeper phreamagmatic interactions in the bedrock that result in violent explosive eruptions that blast out primarily rock fragments, leading to the lower rim.<\/li>\n\n\n\nDiatremes<\/strong> are a subvertical, volcanic pipes (often carrot- or funnel-shaped) formed by phreatomagmatic explosions\/ These explosions fracture the surrounding rock, creating a broad conduit filled with a chaotic mixture of magma fragments, country rock, and juvenile clasts (so-called \u201cdiatreme breccia\u201d). Many maars are the surface expression of a diatreme, which is the subsurface structure feeding a maar, continuing downward from the broad crater.<\/li>\n\n\n\nLittoral cones<\/strong> form when lava enters a body of water or comes into contact with water-saturated ground. Explosive steam generation can hurl molten spatter and fragments upward, forming cones that consist of abundant spatter in addition to ash. They often form when a large front of lava enters the sea, such that not all the lava is explosively converted to ash and tephra.<\/li>\n\n\n\nRootless cones<\/strong> form when lava flows over water-saturated ground (like marshes or wetlands). Steam explosions occur within or just beneath the lava flow, ejecting spatter and creating small cone-like features not fed directly by a magma conduit.<\/li>\n<\/ul>\n\n\n\n